1. Field of the Invention
The present invention relates to an AC generator for use in a vehicle and, in particular, to an AC generator for use in a vehicle capable of improving the cooling performance by preventing interference of the air for cooling the regulator or rectifier which are heat generating parts.
2. Description of the Related Art
FIG. 11 is a cross-sectional view of the arrangement of conventional AC generator for use in a vehicle.
In the conventional AC generator, a rotor 7 is rotatably fitted within a case 3 comprising a front bracket 1 and a rear bracket 2 each made of aluminum by way of a shaft 6 while a stator 8 is fixed on the inner surface of the case so as to cover the outer periphery of the rotor 7.
The shaft 6 is rotatably supported by mean of the front bracket 1 and the rear bracket 2. A pulley 4 is fixed to one of the shaft 6 so that the rotational torque of the engine may be transmitted to the shaft 6 by way of a belt (not shown).
A slip ring 9 for supplying the current to the rotor 7 is fixed to the other end portion of the shaft 6, and a pair of brushes 10 are accommodated within a brush holder 11 disposed within the case 3 so as to come in sidable contact with the slip ring 9. A regulator 18 for regulating the output voltage of the stator 8 is adhered to a heat sink 17 fitted on the brush holder 11. A rectifier 12 is mounted within the case 3 and is electrically connected to the stator 8 to rectify the AC current generated in the coil of the stator 8 into the DC current.
The rotor 7 is comprised of a rotor coil 13 for generating the magnetic flux when a current flows therein, and a pair of pole cores 14 provided so as to cover the rotor coil 13 and be magnetic poles as a result of the magnetic flux generated by the rotor coil 13. Further centrifugal fans 5 are fixed to both axial ends of the rotor 7.
The stator 8 is formed by a stator core 15 and a stator coil 16 achieved by winding a conductor wire around the stator core 15, in which the AC current is generated by alternating the magnetic flux of the rotor 7 with the rotation of the rotor 7.
Next, the arrangement of the brush holder 11 is described with reference to FIGS. 12 through 14.
The brush holder 11 is molded from insulating resin, and is integrally molded with an annular shaft receiving portion 19, a circuit accommodating portion 22, a connector portion 23 and a condencer accommodating portion 24. Inserted conductors are insert-molded into the brush holder 11. The inserted conductors constitute wiring paths between each of the elements mounted in the brush holder 11, as well as projecting into the connector portion 23 to form connecting terminals 23a, and are exposed where necessary to form connecting terminals 34, etc., for electric junction to the rectifier 12. Further, the brushes 10 are accommodated within the brush holder 11 such that one end of each of the brushes 10 protrudes into the shaft receiving portion 19.
Further, a ceramic substrate 21 mounted with diodes and semiconductors, etc., and served as the regulator 18 is secured by adhesive to either one surface of the heat sink 17. The heat sink 17 is disposed with the circuit accommodating portion 22 so that the ceramic substrate 21 is positioned within the circuit accommodating portion 22, and the heat sink 17 and edges portions of the circuit accommodating portion 22 are sealed. The ceramic substrate 21 and the exposed electric junction of the inserted conductors are electrically interconnected, and the sealing resin is poured into the circuit accommodating potion 22 for hardening. Further, on the other surface of the heat sink 17, a multiplicity of fins are provided side by side. Still further, in order to eliminate electrical noise, a condenser 29 is accommodated within the condenser accommodating portion 24.
With this brush holder 11, the circuit accommodating portion 22, the connector portion 23 and the condenser accommodating portion 24 are disposed so as to substantially scatter on a plane, which intersects at a light angle with the axial center of the shaft receiving potion 19, in the circumferential direction thereof in such a way that they do not overlap each other in the axial direction of the shaft receiving portion 19. The heat sink 17 is disposed so that the longitudinal direction of the fin (the fin located at the central portion) directs toward the axial center of the shaft receiving portion 19.
Next, the construction of the rectifier 12 is described with reference to FIG. 15.
The rectifier 12 comprises a pair of arc-shaped heat sinks 31a, 31b each having positive and negative diodes 32a, 32b plurally mounted on the main surface thereof, and an arc-shaped circuit board 33 in which a number of conductors are insert-molded into insulating resin. The pair of heat sinks 31a, 31a are arranged coaxially with their main surfaces lying substantially in the same plane, and the circuit board 33 is arranged on the main surfaces of the pair of heat sinks 31a, 31b so that they constitute the arc-shaped rectifier 12 integrally. The conductors constitute wiring paths between the diodes 32a, 32b, as well as being exposed where necessary to form connecting terminals 33a for electric junction to the connecting terminals 34 of the brush holder 11. Provided on the rear surface of the heat sink 31a are a multiplicity of fins with their longitudinal direction directed in the radial direction.
Here, the rear bracket 2 is made in the form of a bowl by casting or aluminum die casting. As shown in FIG. 16, a rectifier accommodating portion 20a, a condenser accommodating portion 20b, a regulator accommodating portion 20c and a connector accommodating portion 20d are recessed on the inner surface of the rear bracket 2, and intake openings 2a, 2b, 2c for ventilation and a connector receiving hole 2d for receiving the external connector are provided so as to communicate the rectifier accommodating portion 20a, the regulator accommodating portion 20c and the connector accommodating portion 20d with the exterior.
As shown in FIG. 17, the rectifier 12 is positioned within the rectifier accommodating portion 20a and the circuit accommodating portion 22, connector portion 23 and condenser accommodating portion 24 are positioned within the regulator accommodating portion 20c, the connector accommodating portion 20d and the condenser accommodating portion 20b, respectively, so that the rectifier 12 and the brush holder 11 are incorporated into the rear bracket 2. That is, the rectifier 12 and the brush holder 11 are ) incorporated into the substantially identical plane so as to surround the shaft 6.
In the conventional AC generator arranged as above, the current is supplied to the rotary coil 13 from a battery (not shown) by way of the brushes 10 and the slip rings 9, and a magnetic flux is generated. The claw-shaped magnetic poles of the pair of pole cores 14 are magnetized to N polarities and S polarities by the magnetic flux, respectively. On the other hand, the rotational torque of the engine is transmitted to the shaft 6 by way of the belt and the pulley 4, and the rotor 7 is rotated. Thus, a rotational magnetic field is imparted to the stator coil 16 and the electromotive force is generated in the stator coil 16. This AC electromotive force is rectified to a DC current by way of the rectifier 12, its voltage is regulated by the regulator 18, and the battery is recharged.
While the AC generator is generating electricity, the rotor coil 13, the stator coil 16, the rectifier 12 and the regulator 18 generate heat constantly. In the AC generator belonging to a class of rated output current 100A, the heat generation of the rotor coil 13, the stator coil 16, the rectifier 12 and the regulator 18 is each 60 W, 500 W, 120 W and 6 W at points where the temperature is high. Therefore, in order to cool the heat generating by electrical generation, the intake openings are provided at the front bracket 1 and the rear bracket 2.
First, at the rear side, as shown in FIG. 18 by arrow, the external air is sucked from the intake openings 2a, 2b, 2c into the rear bracket 2 under the action of the centrifugal fan 5 provided at the rotor 7. The external air sucked from the intake openings 2a,2b, 2c, as shown in FIG. 19 by arrow, flows toward the edge of the inner circumference of the hear sinks 17, 31a along the fins of the heat sinks 17,31a, subsequently flows from the edge of the inner circumference of the heat sinks 17, 31a toward the front bracket 1 along the axis, and thereafter, bent in the centrifugal direction by means of the centrifugal fan 5 to be discharged to the exterior from the exhaust openings 2e of the rear bracket 2. At this time, the heat exchange between the air flowing along the fins of the heat sinks 17, 31a and the heat sinks 17, 31a suppresses the elevation of temperature of the diodes of the rectifier 12 and the power transistors of the regulator 18, which are the source of heat generation. Likewise, the air bent in the centrifugal direction by the centrifugal fan 5 cools the rear end of the stator coil 16 to suppress elevation of the temperature of the stator coil 16.
On the other, at the front side, the air sucked from the intake openings la of the front bracket 1 is bent in the centrifugal direction by means of the centrifugal fan 5 to cool the front end of the stator coil 16 to be discharged to the exterior from the exhaust openings lb of the front bracket 1.
In the conventional AC generator, since the regulator 18, the connector portion 23, the condenser 29 and the rectifier 12 are arranged in a scattered manner in the circumferential direction on the plane intersecting at a right angle with the axis center of the shaft 6 so that they do not overlap each other in the direction of the axis center, the cooling air is sucked from the intake openings 2a, 2b, 2c of the rear bracket 2 to cool the regulator 18 and the rectifier 12, and after passing around the shaft 6, is discharged in the radially outward direction.
However, the incorporated parts are of complicated form, and the boundary surfaces between the rectifier 12 and the connector portion 23 of the brush holder 11 and between the rectifier 12 and the condenser accommodating portion 24 of the brush holder 11 as viewed in the circumferential direction takes a complicated separate form while there is no member for blocking the circumferential flow of the cooling air which has cooled the rectifier 12 and the regulator 18, so that the cooling air streams flowing along the boundary surfaces become unstable in regard to its direction, which causes counterflow of the warm cooling air after cooling to exert an adverse effect on the cooling of the other heat generating portion, or causes mutual interference of the air streams leading to the loss of pressure with decrease of the amount of cooling air thus degrading the entire cooling performance.
Further, with miniaturization of the AC generator, its components tend to be disposed at adjacent positions in the radial and circumferential direction as well as even in the direction of axis, which eases unevenness of the cooling air stream more and more to degrade the entire cooling performance.
Further, the connector portion 23, which is not the heat generating portion, is inserted with the external connector 30 from the exterior, as shown in FIGS. 20 and 21. Therefore, a connector receiving hole 2d is provided at a position of the rear bracket 2 facing the insertion hole of the connector portion 23, and the unnecessary outflow of the cooling air or the wasteful air inflow not lending itself to cooling also takes place from a gap A between the connector receiving hole 2d and the connector portion 23 and between the connector receiving hole 2d and the external connector 30 to exert an adverse effect on the cooling of the heat generating portions.
Still further, in the foregoing AC generator shown in FIG. 11, each part is accommodated within the bowl-shaped rear bracket 2, but as shown in FIG. 22, there is also an AC generator in which each part is accommodated between the rear bracket 2A and the rear cover 26. In this AC generator, the rectifier 12 and the brush holder 11 are arranged circumferentially in a scattered manner on a plane intersecting at a right angle with the axial center of the shaft 6, as in the foregoing case, so that they are disposed on the rear bracket so as not to overlap each other in the direction of the axis center. Therefore, the air sucked from the intake openings 26a of the rear cover 26b under the action of the centrifugal fan 5, as shown in FIG. 22 by arrow, cools the rectifier 12 and the regulator 19, passes through their edge of the inner circumference of the rectifier 12 and the regulator 19 to flow in the axial direction, and then flow through the intake openings 2f of the rear bracket 2A into the rear bracket 2A. Thereafter, it is bent in the centrifugal direction by means of the centrifugal fan 5 to be discharged from the exhaust openings 2g to the exterior. As described above, also in this AC generator, the cooling air which has cooled the rectifier 12 and the regulator 18 flows in the axial direction, which leaves a problem as with the AC generator of FIG. 11.